1. Field of the Invention
This invention relates to silver halide photographic materials having improved anti-static properties. More particularly the present invention relates to silver halide photographic materials comprising a support with at least one light-sensitive silver halide emulsion layer thereon and at least one anti-static layer thereon and to a method for prevention of the generation of static charges in a photographic material.
2. Description of the Prior Art
Electrostatic charges tend to accumulate on a photographic material during the production and the use thereof, thus causing a number of disadvantages. This generation of electrostatic charges takes place during the manufacturing procedures when the photographic material is brought into contact with rollers in the production line, or when the photographic material is wound up into or unwound from a roll whereby friction and separation occur between the emulsion-coated side and the opposite side to the emulsion-coated side of the photographic material. After the photographic product is delivered to the consumer, on the other hand, electrostatic charges tend to be generated when the photographic product is exposed to very high humidity conditions sufficient to cause adhesion between the emulsion-coated surface and the opposite surface thereof and both surfaces are separated later, or when the photographic product is run in a movie camera or processed in an automatic processor such as, for example, an X-ray film processor. When the accumulated electrostatic charges discharge, the photographic product is undesirably exposed to give rise to irregular static marks comprising spotty, arborescent or feather-like patterns and the like after development. Since these static marks are undetectable until after processing and deteriorate the commercial value of the photographic product to a great extent, the generation of static marks has been a very serious difficulty encountered in the photographic industry and the problem is quite difficult to solve. Further, the accumulated charge tends to attract dust onto the surface of the photographic material, which becomes a cause of secondary difficulties such as coating non-uniformity. It should further be noted that the probability for static marks to occur is sure to increase as the processing speed is increased and as the photographic speed of the emulsion is increased, since most of the supports for photographic products are hydrophobic and sufficiently electrically insulating that electrostatic charges accumulate thereon.
Conventionally, a variety of materials have been used to prevent the generation of static charges in photographic materials. Such anti-static agents are, in general, ionically conductive or have a hygroscopic nature, which property imparts to the photographic product an electrically conductive nature, enabling the electrostatic charge to dissipate easily and thus avoiding a drastic discharge of the accumulated charge. These agents can be used individually or in combination. In order to render the support of a photographic material anti-static, the anti-static agents can be directly incorporated into the high-molecular weight material for the support, or can be coated on the support surface. In the latter case, a coating comprising an anti-static agent alone, or a coating comprising a mixture of an anti-static agent and a polymeric material such as gelatin, poly(vinyl alcohol), cellulose acetate, poly(vinyl butyral), poly(vinyl formal), etc. can be applied to the support. Additionally, the anti-static agent can be incorporated into various layers provided on the support such as the light-sensitive emulsion layer, and other non-light-sensitive, auxiliary layers (e.g., a backing layer, an anti-halation layer, intermediate layers, a protective layer, etc.) An anti-static agent may be applied on the surface of the processed photographic product for the purpose of preventing dust adhesion during subsequent handling thereof. Most of the anti-static agents well known in the art have not been sufficiently effective for photographic products coated with a highly sensitive photographic emulsion, particularly under low humidity conditions e.g., a relative humidity of 30%, undergo a decline in the anti-static effect provided with the passage of time, have a tendency to cause adhesion difficulties under humid conditions, or have a deleterious effect on photographic performances. Since the majority of known anti-static agents were difficult to apply to photographic products as a result of these reasons, various attempts have been made to use recently synthesized anti-static agents in photographic materials. For example, Japanese Patent Application (OPI) No. 91,165/1973 (corresponding to British Pat. No. 1,388,083) and Japanese Patent Application (OPI) No. 121,523/1974 (corresponding to U.S. Pat. No. 3,876,430) describe silver halide photographic products in which so-called ionene type polymers having dissociable groups in the polymer backbone are used. However, such materials do not exhibit an acceptable level of anti-static capability.